path: root/usr/src/man/man9f/ddi_dma_cookie_iter.9f

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.\" Copyright 2019 Robert Mustacchi
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.Dd December 9, 2019
.Dt DDI_DMA_COOKIE_ITER 9F
.Os
.Sh NAME
.Nm ddi_dma_cookie_get ,
.Nm ddi_dma_cookie_iter ,
.Nm ddi_dma_cookie_one ,
.Nm ddi_dma_ncookies ,
.Nm ddi_dma_nextcookie
.Nd retrieve DMA cookies
.Sh SYNOPSIS
.In sys/ddi.h
.In sys/sunddi.h
.Ft "const ddi_dma_cookie_t *"
.Fo ddi_dma_cookie_iter
.Fa "ddi_dma_handle_t handle"
.Fa "const ddi_dma_cookie_t *cookiep"
.Fc
.Ft "const ddi_dma_cookie_t *"
.Fo ddi_dma_cookie_get
.Fa "ddi_dma_handle_t handle"
.Fa "uint_t index"
.Fc
.Ft "const ddi_dma_cookie_t *"
.Fo ddi_dma_cookie_one
.Fa "ddi_dma_handle_t handle"
.Fc
.Ft "uint_t"
.Fo ddi_dma_ncookies
.Fa "ddi_dma_handle_t handle"
.Fc
.Ft void
.Fo ddi_dma_nextcookie
.Fa "ddi_dma_handle_t handle"
.Fa "ddi_dma_cookie_t *cookiep"
.Fc
.Sh PARAMETERS
.Bl -tag -width Fa
.It Fa handle
The DMA handle obtained by a call to
.Xr ddi_dma_alloc_handle 9F .
.It Fa cookie
A pointer to a
.Xr ddi_dma_cookie 9S
structure.
.It Fa index
An unsigned integer that represents the index of a cookie to obtain.
The first entry is at index zero.
.El
.Sh DESCRIPTION
The
.Fn ddi_dma_cookie_iter ,
.Fn ddi_dma_cookie_get ,
and
.Fn ddi_dma_cookie_one
functions obtain information about DMA cookies.
When a DMA request, represented by the DMA handle
.Fa handle ,
has been bound to a series of addresses with the
.Xr ddi_dma_addr_bind_handle 9F
or
.Xr ddi_dma_buf_bind_handle 9F
functions, the resulting addresses are stored in one or more
.Xr ddi_dma_cookie 9S
structures.
the three different functions provide different ways to obtain cookies
and are safe alternatives to the unsafe
.Fn ddi_dma_nextcookie
function.
To see how to use these functions, please see the
.Sx EXAMPLES
section.
.Pp
The
.Fn ddi_dma_cookie_iter
function provides a way to iterate over all the cookies that are
associated with the DMA handle
.Fa handle .
To get the first handle, pass
.Dv NULL
in
.Fa cookiep .
Do not use the DMA cookie returned from either of the
.Xr ddi_dma_addr_bind_handle 9F
or
.Xr ddi_dma_buf_bind_handle 9F
functions.
To get subsequent cookies, pass the returned cookie as the argument
.Fa cookiep .
When the function returns
.Dv NULL
then that indicates that the last handle has been iterated over.
.Pp
The
.Fn ddi_dma_cookie_get
function returns a specific cookie.
The
.Fa index
indicates which of the cookies should be returned.
The first cookie is at index
.Sy 0 .
If an invalid index is specified, the function returns
.Dv NULL .
.Pp
The
.Ft ddi_dma_cookie_one
function is a convenience function for DMA requests that have a single
cookie.
This function always returns the single cookie assosciated with the DMA
handle
.Fa handle .
If this function is used when there is a DMA request with multiple
cookies, then it will panic the system.
It can never return
.Dv NULL .
.Pp
The
.Fn ddi_dma_ncookies
function returns the number of DMA cookies that are associated with the
DMA handle
.Fa handle .
If there are no DMA resources bound to the handle, then this will return
.Sy 0 .
.Pp
The
.Fn ddi_dma_nextcookie
function was the historical function that was associated with obtaining
DMA cookies.
It should not be used due to several flaws.
The
.Fn ddi_dma_nextcookie
function mutates the underlying DMA handle meaning that a driver cannot
obtain a cookie a second time and thus a device driver using this
interface must either manually keep storage of the cookie around wasting
space or rebind the handle, wasting time.
In addition, there is no way for the function to indicate that a driver
has consumed all of its cookies.
If for some reason a device driver calls the
.Fn ddi_dma_nextcookie
function more times than there are cookies, the results are undefined.
In short, this function should not be used for any purpose.
Use the
.Fn ddi_dma_cookie_iter ,
.Fn ddi_dma_cookie_get ,
or
.Fn ddi_dma_cookie_one
functions instead.
.Sh CONTEXT
The
.Fn ddi_dma_cookie_iter ,
.Fn ddi_dma_cookie_get ,
.Fn ddi_dma_cookie_one ,
.Fn ddi_dma_ncookies ,
and
.Fn ddi_dma_nextcookie
functions may be called from
.Sy user ,
.Sy kernel ,
or
.Sy interrupt
context.
.Sh RETURN VALUES
Upon successful completion, the
.Fn ddi_dma_cookie_iter ,
.Fn ddi_dma_cookie_get ,
.Fn ddi_dma_cookie_one
functions will return the requested DMA cookie.
If there are no more cookies, or
.Fa coookiep
is invalid, the
.Fn ddi_dma_cookie_iter
function will return
.Dv NULL .
If
.Fa index
does not correspond to a valid cookie, the
.Fn ddi_dma_cookie_get
function will return
.Dv NULL .
If there is not exactly one DMA cookie, or another issue occurs, then the
.Fn ddi_dma_cookie_one
function will panic the system.
.Pp
Upon successful completion, the
.Fn ddi_dma_ncookies
function returns the number of cookies associated with
.Fa handle .
If there are none, then
.Sy 0
is returned.
.Pp
The
.Fn ddi_dma_nextcookie
function always updates
.Fa cookiep
regardless of whether it is valid or not.
.Sh EXAMPLES
.Sy Example 1
Using the
.Fn ddi_dma_cookie_iter
function to obtain all DMA cookies.
.Bd -literal
/*
 * This example assumes that either ddi_dma_addr_bind_handle() or
 * ddi_dma_buf_bind_handle() has already been successfully called.
 */
void
program_dma(ddi_dma_handle_t handle)
{
	const ddi_dma_cookie_t *c;

	for (cookie = ddi_dma_cookie_iter(handle, NULL); c != NULL;
	    c = ddi_dma_cookie_iter(handle, c)) {
		/*
		 * Use the dmac_laddress and dmac_size members to
		 * properly program the device or descriptor rings.
		 */
	}
}
.Ed
.Pp
.Sy Example 2
Using the
.Fn ddi_dma_cookie_get
function.
.Bd -literal
/*
 * This example assumes that either ddi_dma_mem_alloc() has already
 * been successfully called.
 */
int
bind_dma(ddi_dma_handle_t handle, void *addr, size_t len)
{
	int ret;
	uint_t i, ncookies;
	ddi_dma_cookie_t first;

	ret = ddi_dma_addr_bind_handle(handle, NULL, addr, len,
	    DDI_DMA_RDWR | DDI_DMA_CONSISTENT, NULL, NULL, &first,
	    &ncookies);
	if (ret != DDI_DMA_MAPPED) {
		return (ret);
	}

	/*
	 * A driver doesn't need to store ncookies. It can get it again
	 * by simply calling ddi_dma_ncookies() and using the result in
	 * place of ncookies from ddi_dma_addr_bind_handle().
	 */
	for (i = 0; i < ncookies; i++) {
		const ddi_dma_cookie_t *cookie;

		cookie = ddi_dma_coookie_get(handle, i);
		/*
		 * Use the dmac_laddress and dmac_size members to
		 * properly program the device or descriptor rings.
		 */
	}
}
.Ed
.Sh SEE ALSO
.Xr ddi_dma_addr_bind_handle 9F ,
.Xr ddi_dma_alloc_handle 9F ,
.Xr ddi_dma_buf_bind_handle 9F ,
.Xr ddi_dma_unbind_handle 9F ,
.Xr ddi_dma_cookie 9S
.Rs
.%T Writing Device Drivers
.Re